Hello, it looks like mahonia rust, and you can spray with a fungcide, it looks like you have pruned it, they do respond to hard pruning, you need to let the air circulate so prune to achieve this, clear up all the fallen deseased leaves and bin them, keep it watered well, more so in long dry spells, cut away some of the damaged leaves too, mahonias do better in partial shade, julien.

Thankyou Julien what fungcide should I use ?

It has been planted in same partial shade for 22years.

Many thanks.